The present invention relates to a fuel injection valve for internal combustion engines, and more particularly to a fuel injection valve in which an ON-OFF switch is constituted by a needle valve and a nozzle body.
In prior art, for the purpose of obtaining electric signals indicating the beginning and completion of fuel injection in accordance with the movement of a needle valve, there have been disclosed various fuel injection valves in which an ON-OFF switch is constituted by a nozzle body of conductive material and a needle valve of conductive material which is capable of smoothly moving in a guide hole defined in the nozzle body (as disclosed, for example, in U.S. Pat. Nos. 4,111,178 and 4,398,670).
In the conventional fuel injection valves disclosed above, an appropriate insulating layer is provided between the needle valve and the guide surface of the guide hole of the nozzle body so that electrical contact occurs between the needle valve and the nozzle body only when the needle valve is seated on the valve seat formed in the nozzle body and a state of complete electrical discontinuity occurs between the needle valve and the nozzle body when the needle valve is lifted upon the application of pressurized fuel.
However, in the conventional fuel injection valve constructed as described above, since there is a probability that the rear end surface of the needle valve temporarily comes into contact with the spacer in the nozzle holder when the needle valve is lifted up to its allowable stroke at the time of the fuel injecting operation, there may occur the disadvantage that noise signals in the form of narrow pulses are superposed on the desired signal obtained from the ON-OFF switch of the fuel injection valve. That is, in the conventional fuel injection valve with an ON-OFF switch, even if the fuel injection valve is in the state of fuel injection, a state similar to the closed condition of the ON-OFF switch occurs momentarily. As a result, in the prior art, it is impossible to obtain a signal indicative of the lift condition of the needle valve, the level of which is maintained at a predetermined level during the fuel injecting operation. Consequently, since it is not possible to easily detect the duration of the open condition of the fuel injection valve on the basis of the signal obtained from the ON-OFF switch, an additional circuit such as a signal discriminating circuit is required.